Dents Run Site 3895

The USACE Baltimore District retained BioMost, Inc. to design passive treatment components to abate abandoned mine discharges associated with the northern site of Problem Area 3895. The site is located in Porcupine Hollow of the Dents Run Watershed, Benezette Township, Elk County, PA. Bid documents were prepared and included specifications, drawings, and cost estimates. Phase I construction was completed in November 2006 and Phase II construction was completed October 2008.

Utilizing selected historical and recent data, BioMost focused on providing a passive system design to treat the most severely degraded abandoned mine drainage in the Dents Run Watershed. The goal is to return the major tributary in Porcupine Hollow to a viable fishery. The design considers (1) economics (implementation costs), (2) effectiveness (degree of treatment), (3) flexibility and accessibility (ability to monitor and to potentially incorporate future technological advancements), (4) sustainability (minimize operation and maintenance requirements), and (5) landowner considerations (relating to elk herd management and land use).

By considering the site holistically, relating to geology, topography, cultural features, land uses, mining history, and drainage characteristics, a design for passive treatment has been completed. This design is for a system that is both economical in implementation and in maintenance.

Water Quality of Site Drainage (Average Values)

Point

Flow
(gpm)

pH

Acidity
(mg/l)

D. Fe
(mg/l)

D. Mn
(mg/l)

D. Al (mg/l)

162-2

5

2.4

2032

404

16

136

162-3

10

2.6

1242

264

15

76

Abandoned mine discharges taken at source.

The passive treatment system design for Phase 1 utilizes and encourages the already naturally-occurring chemical reactions at Site 3895.
Precipitation of iron-bearing minerals at low pH decreases iron and sulfate concentrations and reduces acidity generation and sludge volumes in comparison to treatment at the source with limestone-based systems. By decreasing acidity, the Phase 2 alkalinity-generating components were sized to contain less treatment media. In addition, as the majority of the iron has been removed in Phase 1, the settling ponds/wetlands are designed to be smaller in size for Phase 2. Furthermore, decreasing the sludge volume by generating a more dense precipitate is will result in decreased operation and maintenance expenses over the life of the system. The design also includes implementation of a passive component for onsite net-alkaline mine drainage with an organic treatment media to increase alkalinity through microbial sulfate reduction without increasing dissolved calcium concentrations prior to mixing with the highly acidic drainage. This component has been designed to address gypsum precipitation within the future Phase 2 passive treatment system.

Monitoring planned for the near future is expected to document that “Porcupine Run” is substantially improved and capable of supporting a viable aquatic habitat. By restoring “Porcupine Run” to a water quality having a circumneutral pH, excess alkalinity, and low metals content, the stream flow from Porcupine Hollow instead of degrading Dents Run is expected to significantly contribute to the restoration of Dents Run.